So we're thinking about upgrading from FCP7 and we're looking into both AVID and Premier, our editors have a mix of experience on both.

We're thinking about running mainly with AVID which would work for our Broadcast work perfectly. And then having Premier installed on our suites primarily for fast turnaround work, and high level promotions work where its integration with After Effects would come in particularly handy.

We're keen on having both options to hand but we're wondering what kind of issues we'll run into media management wise. How easy it would be to take a Premier promo sequence from a few weeks ago and push it into an AVID sequence for another show.

We have several Edit Suites (Macs) and MacBook Pros for location work. All our media lives on a central server and gets archived (raw footage and Media Managed shows) onto Data Tape.

We're also looking into getting CatDV set up, don't know whether that can help with the movearound.

I do some tests first. Things have supposed to have gotten better but it's never been an easy process in the past.
I'd rather pull my teeth out with pliers than have to make Premiere and Avid talk to each other...
We have both and use both but we make sure they stay separate. Each job is pitched for the system that suits it best. Jumping between systems is just asking for problems. And as each product evolves workflows that did work break and new workflows become possible. You'll spend your life finding solutions.

Its really down to how tight an integration we need with AE and photoshop. Generally we prefer Media Composer because we know it so well and like the backwards project and media support as we have clients and jobs that go back over a decade. And even if we have After Effects elements with AMA linking in MC we can update and change content easily.

But if we have a job that will need a lot of layers composited together and for that to be adjusted and altered as the job goes on then it's quicker in PPro.

That said I even have FCP=X available here and an editor to drive it and some jobs even suit that. It's just picking the right tool for the job.

On the Premiere side the main concern is the media management, especially for longer form stuff.
And my personal hate is (much as FCP7 had) having just a project file with all my bins and sequences in it. I've seen too many bloated massive project files and even worse the failing to open project file.
AT least with Media Composer you can save and manipulate bins and that can be a job saver...